1. Field of the Invention
The present invention relates to a liquid crystal display device including a reflector, and a portable electronic apparatus. More particularly, the present invention relates to a liquid crystal display device which has a viewing angle property that allows a display to appear brighter when a viewer looks at the display from a direction close to a direction of a normal line with respect to a display surface of the liquid crystal display device than when the viewer looks at the display from other viewing angles; and a portable electronic apparatus including at its display section the liquid crystal display device with such a viewing angle property.
2. Description of the Related Art
In general, liquid crystal display devices are called semi-transmissive liquid crystal display devices or transmissive liquid crystal display devices, which include backlights, or reflective liquid crystal display devices, depending upon the form of display of the liquid crystal display devices. To display images, reflective liquid crystal display devices use only outside light, such as sunlight or light from indoor illumination sources, and, thus, do not use a backlight. Reflective liquid crystal display devices are frequently used in, for example, portable information terminals that are under constant stress to be made thinner and lighter and to have decreasing power consumption.
When semi-transmissive liquid crystal display devices are in an environment that does not provided sufficient outside light, a backlight is turned on for operation in a transmission mode. On the other hand, when semi-transmissive liquid crystal display devices are in an environment that provides sufficient outside light, the backlight is not turned on, so that they operate in a reflection mode thereby saving power. Semi-transmissive liquid crystal display devices are frequently used in portable electronic apparatuses, such as cellular phones or notebook-size personal computers (PC).
FIG. 12 is a sectional view of an example of a related transflective liquid crystal display device.
In the general structure of the transflective liquid crystal display device, a reflection mode STN (super-twisted nematic) liquid crystal cell 72, a forward scattering plate 90, an upper retardation plate 73b, and an upper polarizing plate 74 are placed upon each other on a lower retardation plate 73a of a reflective plate 71 in that order from the side of the lower retardation plate 73a; and a backlight 95, serving as a light source, is provided below the reflective plate 71. The reflective plate 71 has a lower polarizing plate 70 and the lower retardation plate 73a provided thereat.
In the general structure of the liquid crystal cell 72, a lower glass substrate 75, a color filter 76, a lower transparent electrode layer 78, a lower alignment film 79, an upper alignment film 80 disposed so as to be separated from and to oppose the lower alignment film 79, an upper transparent electrode layer 81, and an upper glass substrate 82 are placed upon each other in that order from the side of the lower polarizing plate 70. A super-twisted nematic liquid crystal layer 83 is disposed between the lower and upper alignment films 79 and 80. An overcoat layer (not shown), formed of silica or acrylic resin, is provided between the color filter 76 and the lower transparent electrode layer 78.
The reflective plate 71 has an A1 film whose surface is in a specular state, and has holes 71a for passing light from the backlight 95 when the backlight 95 is used.
The retardation plates 73a and 73b are provided to prevent coloring of the display into blue or yellow by compensating for phase differences of light that passes through the STN liquid crystals.
The forward scattering plate 90 is causes the incident light to be reflected not only in a specular reflection direction by the surface of the reflective plate 71, but also in a direction close to the specular reflection direction by the surface of the reflector 71. The forward scattering plate 90 achieves this by scattering light (outside light) passing through the upper polarizing plate 74 and the upper retardation plate 73b and incident upon the forward scattering plate 90 towards the liquid crystal cell 72.
FIG. 13 illustrates another example of a related transflective liquid crystal display device.
In the general structure of the transflective liquid crystal display device, a first retardation plate 173a, a second retardation plate 173b, and a polarizing plate 174 are placed upon each other on a reflection mode STN (super-twisted nematic) liquid crystal cell 172 in that order from the side of an upper glass substrate 182; and a backlight 195, serving as a light source, is provided below the liquid crystal cell 172.
In the general structure of the liquid crystal cell 172, a lower glass substrate 175, a reflector 171, an overcoat layer 171c, a color filter 176, an overcoat layer 177a, a lower transparent electrode layer 178, a lower alignment film 179, an upper alignment film 180 disposed so as to be separated from and to oppose the lower alignment film 179, a topcoat layer 177b, an upper transparent electrode layer 181, and an upper glass substrate 182 are placed upon each other in that order.
Many minute bumpy portions (recesses 171e in FIG. 13) are formed adjacent each other in an irregular manner at a reflective surface of the reflector 171. The bumpy portions can be formed by, for example, conventional photolithography methods. In one such method, a surface of a resin base material 171a, such as a photosensitive resin layer, is irradiated with light through a mask pattern, the exposed resin is developed to form many minute adjacent spherical recesses, and the surface of the resin base material 171a having the spherical recesses is subjected to evaporation or plating using, for example, aluminum or silver in order to form a metallic film 171b having the bumpy portions (the recesses 171e).
The metallic film 171b can be made thin (to a thickness of the order of 30 nm) so that light from the backlight 195 can pass therethrough when the transflective liquid crystal display device is in a transmission mode.
The inside surfaces of the recesses 171e are spherical, and have an inclination angle distribution in a range of from −20 degrees to +20 degrees and a depth within a range of from 0.1 μm to 3 μm. Distances between the recesses 171e are set so that pitches between adjacent recesses (center-to-center distance) differ within a range of from 5 μm to 50 μm.
To achieve satisfactory display performance of a liquid crystal display device, it is ordinarily necessary for factors such as (1) resolution, (2) contrast, (3) brightness of a screen, (4) brightness of color, and (5) visibility (viewing angle wideness) to be satisfactory.
As shown in FIG. 14, a liquid crystal display device which is incorporated in an apparatus which is used with its display surface inclined, such as a portable information terminal including a cellular phone or a notebook-size personal computer, is frequently viewed from a direction close to a normal line direction P with respect to the display surface. More particularly, the information terminal is frequently viewed from a direction within a range of about 10 degrees from the normal line direction P. In general, an angle θ between a main viewing direction α when a viewer (user) views the display surface (screen) and the normal line direction P is frequently within a range of from about 0 degrees to about 20 degrees.
FIG. 14 illustrates a state in which a cellular phone including a display section 100 which comprises a liquid crystal display device and which is provided in a body 105 is being used. In FIG. 14, reference character P denotes the normal line with respect to the display surface of the display section 100, reference character Q denotes incident light, and reference character ωo denotes an incidence angle (such as about 30 degrees) of the incident light from the normal line. Reference character R1 denotes reflected light (specularly reflected light) when the incidence angle ωo and a reflection angle ω are equal from the normal line, reference character R2 denotes reflected light when the reflection angle ω is smaller than the incidence angle ωo from the normal line, and reference character R3 denotes reflected light when the reflection angle ω is greater than the incidence angle ωo from the normal line.
As can be seen from FIG. 14, a viewing point Ob of the viewer is concentrated ordinarily in the reflected-light-R2 direction close to the normal line direction P, specifically, in a direction within a range of up to about 10 degrees from the normal line direction P. In contrast, the reflected light beams R1 and R3 are such as to cause the viewer to look at the display surface from the lower side to the upper side, thereby making it difficult for the viewer to see what is displayed on the display surface. Therefore, it is desirable to provide a wide viewing angle and, at the same time, to increase the reflection ratio of the liquid crystal display device in a direction where the reflection angle is smaller than a specular reflection angle.
However, when the related liquid crystal display device shown in FIG. 12 is in a reflection mode, the range in which incident light is reflected is wider than that of a liquid crystal display device of the type that does not include a forward scattering plate, but most of the incident light is reflected in the specular reflection direction and in directions near the specular reflection direction (reflection ratio peak value occurs at a specular reflection angle or at angles close to the specular reflection angle). Therefore, when the viewer views the display section from the specular reflection direction and in directions close to the specular reflection direction, what is displayed on the display section appears bright. However, when the viewer views it from other directions, what is displayed on the display section appears dark.
In the related liquid crystal display device shown in FIG. 13, a large portion of the incident light is reflected in the specular reflection direction and in directions close to the specular reflection direction (peak value of the reflection ratio occurs at the specular reflection angle or at angles that are slightly greater than or less than the specular reflection angle). Therefore, when the viewer views the display section from the specular reflection direction and from directions close to the specular reflection direction, what is displayed on the display section appears bright. However, when the viewer views it from other directions, what is displayed on the display section appears dark.
Accordingly, since, as mentioned above, the viewing point of the viewer is ordinarily concentrated in directions close to the normal line direction P when the display surface of, for example, a cellular phone including any one of the related transflective display devices at the display section is viewed, the display appears dark. When the viewer tries to view the display so that it appears bright, the viewer must view the display from the specular reflection direction or directions close to the specular reflection direction, in which case, as mentioned above, the viewer views the display surface upward from the lower side to the upper side, thereby making it difficult to see what is displayed on the display section. Thus, typical users require not only a broader range of viewing angles (with sufficient brightness), but also increased brightness specifically at a range of typically used viewing angles (relatively close to the normal line of the display) than that provided from conventional displays.